Devices and methods for sustained intraocular delivery of drugs are described in numerous U.S. patents. U.S. Pat. No. 6,331,313 (Wong et al.), discloses an orificed impermeable outer layer surrounding a core of drug for intraocular delivery and references additional patents on the art. U.S. Pat. No. 5,902,598 (Chen et al.) discloses multiple coating layers surounding an inner drug core or reservoir and providing permeability and openings for intraocular drug delivery, and references additional patents on the art. U.S. Pat. No. 5,378,475 (Smith et al.) discloses a suture tab attached to coating layers surounding one or more drugs core or reservoir and providing permeability and openings for intraocular drug delivery, and references additional patents on the art.
In non-intraocular sustained delivery systems for drugs, U.S. Pat. No. 5,795,591 (Lee et al.), among other patents, discloses the use of laser drilling to produce orifices through which the drugs may be delivered.
One method of delivering drugs in an intraocular site uses a suture tab attached to a capsule or cup containing the drug. The suture tab is typically made of polyvinyl alcohol (PVA), which is hydrophilic. The suture tab is inserted in the vitreous region of the eyeball and attached to the inner surface at a location appropriate for delivery of drug to a desired target area, such as the retina. The cup containing the drug is typically made of polydimethyl siloxane (PDMS), which is hydrophobic, making it impermeable to the drugs to be delivered. The controlled delivery of the drug from the cup requires one or more apertures in the PDMS through which the drug passes out of the cup, and requires some means of restricting drug flow through the aperture or apertures. In addition, drug delivery must be consistent among different capsules, and must be consistent for any individual capsule throughout the period of delivery.
To address these requirements, each cup is fabricated with a hole in the PDMS through which the drug is delivered, and a layer of PVA is placed between the drug and the hole. The PVA, being hydrophilic, is permeable to the drug. The drug diffuses through the PVA and passes through the hole into the vitreous region of the eye. Clearly the hole size and shape must be consistent, and the pathway through the hole must be unobstructed, for appropriate rates of drug delivery to be achieved and sustained. In addition, the proximity of hydrophilic PVA to hydrophobic PDMS cannot be allowed to introduce obstacles to drug delivery due to surface tension and consequent meniscus between them.
The conventional process used to cut the hole is a manual process using tools. This process leads to variations in size and position (centering on the cup top), and results in excess material around the cut either from flash or the material from the hole not being fully removed. These variations could potentially cause significant variations in the drug dosage received by the patient. Cutting the hole post extraction is preferable, however, cutting with a tool would lead to possible contamination in a process where less handling would be preferred from a microbiological viewpoint. The primary problem that must be solved is the formation of the hole in the PDMS cups with precise dimensions, clean cuts, reproducibly and with a process that is capable of being automated.